The present invention is concerned with a brake pressure regulator for a hydraulic brake system for automotive vehicles to perform anti-locking control (ALC-mode) and traction skid control (TSC-mode), comprising a master cylinder, a pressure modulation aggregate for changing the hydraulic pressure in the wheel cylinders (wheel cylinder pressure modulator), an electronic regulator and wheel sensors generating sensor signals received by the electronic regulator at the input thereof, processing the same in accordance with one or more control algorithms, and rendering the same available at the output thereof as corrective variables for the wheel cylinder pressure modulator, and further comprising a pressure fluid source generating a hydraulic source pressure, a pressure fluid reservoir, a hydraulic brake force booster which, upon actuation of the brake pedal, generates a controlled hydraulic pressure (booster pressure).
In modern automobile engineering, the use of automatically controlled brakes is increasing to provide for enhancing the driving stability. Anti-locking devices are already being assembled in large numbers. Added thereto is the traction control of the automotive vehicle, i.e., the control of the pressure in the wheel cylinders of actuated or driven wheels during start-off or during acceleration. Racing or loss of traction of the driven wheels is to be precluded and the driving stability to be increased thereby. This will especially apply in the event of low coefficients of traction of the road surface and abrupt changes in the coefficient of friction or split.
Two general practices exist for controlling the traction skid:
First, traction control with no gearing, i.e. in the absence of so-called "engine management". In this method of control, only the brake or, stated more precisely, the modulated pressure in the wheel cylinders of the brake, is used for traction control. This process is referred to as the "Brake Blocking Differential" or, in abbreviated form, as "BBD".
Secondly, the combination of control through the brake as described above and simultaneous control in the presence of "engine management".
In engine management, the torque of the internal combustion engine is changed by a change in the rate of fuel injection, by a change in the throttle valve position, by switching on and off the whole ignition or individual spark plugs only, by ignition timing adjustment or by other means.
Hence, the traction, on the one hand, is controlled by applying the brake and, on the other hand, by switching off or reducing the engine torque.
The second-method of control, in recent usage, is called "traction skid control" or "TSC", although former usage referred to traction skid control as a control method described under the first method.
All statements made in the claims and in the description hereinafter relative to traction skid control, for reasons of simplification, also apply to brake blocking differential control.
The development in modern automobile engineering, tends to control the torque on the wheel of the automotive vehicle both in the decelerating event (anti-locking control) and in the traction event (BBD-control and traction skid control, respectively).
Efforts are being made on the part of the automotive industry to improve the anti-locking devices by traction skid control means. The combination of anti-locking devices and traction skid control means is generally speaking known in the art.
Reference is made, for example, to German Patent Application P 3611931.
The German Patent Application P 36 11 931 refers to a hydraulic brake system with wheel skid control means, especially for use with automotive vehicles. The system includes a master cylinder pressurizable by a hydraulic force booster, wherein valve means are provided between the master cylinder and the wheel brakes connected to the master cylinder. Pressure fluid is withdrawable from the wheel brakes through the valve means, with pressure fluid withdrawn from the wheel brakes being replenishable from the pressure chamber of the hydraulic force booster or from an auxiliary pressure source, and wherein, during the control process, the stroke of the brake pedal is limited.
The special features of the wheel skid control means reside in pressure conduits connected to the brake conduits leading from the working chambers of the master cylinder to the wheel brakes. The pressure conduits are capable of being connected to the pressure chamber of the hydraulic booster and/or to the auxiliary pressure source through the valve means. Check valves are provided in the brake conduits through which the connections of the brake conduits in the working chambers of the master cylinder can be interrupted.
In traction skid control means of the type described above, substantial efforts in terms of valves are involved. The use of a plurality of magnetic valves is required to insure faultless operation of the system in the traction skid control mode. In this connection it is to be taken into consideration that, in the traction skid control mode, some parts of the anti-locking device are to be hydraulically separated from the traction skid control components. However, conversely, the pressure fluid supply for the traction skid control is to be safeguarded. These requirements make the use of several electromagnetic valves imperative.
German Patent Application 36 38 047 discloses a hydraulic brake system with brake and traction skid control for use with automotive vehicles. The system includes a pedal-operated brake presure operator consisting of a master brake cylinder, a force booster and a pressure source. Valves are connected to the wheel brakes and are controlled by skid control means.
In the afore-described brake system a pressure reducing valve is coupled to the pressure source. The pressure reducing valve is actuated either by the pressure in the booster chamber or, if the pressure in the booster chamber is low, by a predetermined force so that the pressure of the booster chamber or a pressure corresponding to the predetermined force prevails in the outlet chamber of the pressure reducing valve.